Embedded fiber wallboard



Dec. 2l, 1954 A. ELMENDORF 2,697,677

EMBEDDED FIBER wALLBoARn Filed Ilarch 12, 1952 fnyenzar .Ir/22)?ZY/2261207029 /Ote- 670`v United States Patent O EMBEDDED FIBERWALLBOARD Armin Elmendorf, Winnetka, Ill.

Application March 12, 1952, Serial No. 276,071

6 Claims. (Cl. 154-453) The present invention is the result of prolongedresearch work aimed at overcoming some of the objections and liabilitiesinherent in the type of fire-resistant wallboard commonly called gypsumboard, consisting of two layers of thick paper bonded to a core ofgypsum. Such boards are generally 3i-inch or 1/z-inch thick, andtherefore differ in thickness from the conventional lath and plasterthickness which is about %inch.

In comparison with other types of board, such as plywood, hardboard andinsulation board, the gypsum boards are relatively inexpensive, but inorder to obtain a wall having a smooth, hard surface it is necessary toapply plaster to gypsum boards after application.

The paper surface is readily scutfed, and it is difficult to make ajoint between board edges with a texture similar to that of the paper.

Due to the difference in the strength properties of the paper in themachine and across-the-machine direction, the strength of plaster-boardacross-the-rnachine direction of the paper may be less than half thestrength in the machine direction of the paper. As such boards arenormally applied with the machine direction parallel to the studdingthey are relatively weak in the direction where strength is mostimportant, namely, across the studding. It would be desirable if suchwallboards had the same strength in all directions.

Large-headed nails must be used to hold paper-faced gypsum boards firmlyto the wood framing. Such nails disfigure the wall and reduce the valueof the board for interior decoration.

Most of the strength of paper-faced gypsum boards lies in the facingsheet. If this has been broken the board has very little residualstrength left. When stressed they are therefore readily ruptured, andthey fail abruptly and completely. The boards in place are readily bentand are lacking in stiffness.

When subjected to a fire the paper faces are quickly burnt away, therebyexposing the gypsum core, which, upon losing its water ofcrystallization, shrinks and develops cracks that permit the oppositesurface to heat and disintegrate.

As an embodiment of my invention, or as the result of my method, Iillustrate, in perspective, with a cross-section, a part of a sheet ofmaterial produced in accordance with my invention. The showing is, in abroad sense, diagrammatic, since it is impossible precisely to show in adrawing the specific structure or variety of structure which resultsfrom the employment of my method.

With reference to the drawing, as shown, 1 generally indicates a sheetof material having opposite and generally parallel surfaces 2 and 3. Theforward face of the figure is a diagrammatic illustration of a typicalsection. It will be understood, of course, that, in detail, the sectionmay vary widely, but the characteristics of such a section are thoughtto be properly shown. It will be observed that the surface 1 iscompletely free of any projecting ends of fibrous material, but that afibrous material appears scattered throughout the section. Theindividual fibres, for convenience, are identified by the numeral 4. Thesurface zones at opposite sides or faces of the sheet are indicated at aand b, and the central zone, between the zones a and b, is indicated asc.

Stated briey, my product consists of a binder, generally indicated as 5,in which are embedded fshort, strandlike fibres of wood, as indicated at4. In the surface zones d and b t e vo urne of the binder 5 exceeds thevolume of the fibres... In thecentral .zone c fthe volume of the fibresICC preferably exceeds the volume of the binder. The ,concentration ofthe binder increases progressively from the boundaries oftlie zone c, tothe surface of the board, but

many of'tlie b'res of'tli'zone'c extend into the zones a and 5 b, therebeing no exact or rigidly outlined separation between the two zones. Aswill be clear from the drawing, the average angles of the fibres in thezones a and b, relative to the plane of the board surface, is less than45 degrees. Note, also, that, preferably, as shown in the drawing, thethickness of the zone c exceeds the sum of the thicknesses of thesurface zones a and b.

In boards rnade in accordance with my invention the p e, y exce siorres, and they are substantially shorter than excelsior fibres.

wood shavin s in which the botanic fibres of the-WM5 substantiallyparallel to ming' s ntlugliout'the eng o t e s avings. e engt may vary,but I prefer a Engl? gi jnch to 6 inchesE with the width of theshavingspre erab y very ess an theirl length. These shavings, forexample, may be employed in strands of 00 inch thickness. For the testsbelow set out I selected c sa pine or he shavin s, the sawdust and forwhat mn strands of the present invention. Comparable mds were used forthe other fibres.

As a binder I may employ any suitable ent I may employ, for example, amatrix o l gpsum, Eu-t my method is applicable to binders other thangypsum.

In manufacturing my board it will be understood that the binder may becompletely opaque, or, if desired, may be partially translucent, or evenapproach transparency when in a thin layer. Thus the fibres in thesurface layers a and b, which approach but do not reach the surface ofthe board, may, under some circumstances, be visible through the matrixor binder, or may be traceable by a slight discoloration of the binderor matrix by solubles in the wood of which the fibres or shavings aremade. It will be understood that I do not wish to be limited to anyspecific method of making libres or shavings, and, in fact, an importantpurpose of my invention is to permit the use of fibres or shavings whichare byproducts. I may employ, for example, such shavings as are producedby a rip-saw tooth of a large saw. The shavings produced by shingle sawsmay be used advantageously. In considering advantageous materials for mypurpose, short, narrow ribbons of wood, not necessarily fiat, areadvantageous, and may be an inch or more in length, but much shorterthan the long, curly strands of excelsior.

A substantial advantage of the board of the present invention includesthe fact that the cost of the materials comprising the new board is lessthan the cost of those used for conventional gypsum'boards. The newboard is therefore superior to ordinary gypsum board in the followingrespects:

l. The surface is hard and smooth, and it will not scuff. Whilewallpaper cannot be removed from ordinary gypsum board without damagingthe board surface, the new board acts like a conventional plaster wallin this respect, and

old wallpaper can be readily scraped off.

2. Any crack filling that may be required at the joints can be done witha filler similar in hardness and appearance to the board surface so thatthe change in texture at the joint associated with ordinary paper-facedgypsum board installations is eliminated.

3. The strength properties are the same lengthwise as across the board.

4. Nails with much smaller heads can be used for applying the board, andthere is no dipping in of the board around the rim of the nail head;hence, the disfiguring effect of the nails used for applying wallboardsis greatly reduced.

5. Fibrous facing sheets are not necessary for strength, and as thecomposition of the board is substantially the same throughout itsthickness, it is not liable to surface injury which would weaken theboard.

6. It is stronger and much more resistant to breakage in place, and willabsorb a much greater blow than paper-.faced gypsum boards.

so 7. It is much stiffer. and. therefore deflects much less under a pushapplied to thewallbetween studs.

I employ strand-like 8. It is more tire-resistant than paper-facedgypsum boards.-

9. The combined materials cost of the new board is lsauobstintially lessthan that of the paper-faced gypsum ar s.

The elimination of the paper facing of conventional gypsum boards andthe results described above were achieved by the use of a newstrand-like shaving perfected by the inventor, which can be used notonly in combination with gypsum but also with other types of inorganicbinders, such as Portland cement and magnesite cement, withsubstantially the same results. The improvements listed are particularlystriking when a substantially non-porous board is made in which thebinder serves as a matrix to fix the dimensions and surface of theboard, and the iibers are interspersed in the matrix.

While the art of combining inorganic binders, such as cement withsawdust and Shavings, is old and the art of combining excelsior with thesame binders is a well-established practice for the manufacture ofporous fibreboards, no one, to my knowledge, has ever developed asuccessful solid, non-porous board to date, because no board made withcurrently known wood particles or bers has the necessary physical andstrength properties which would make it competitively superior to otherboards on the market and, in particular, superior to conventional gypsumboards.

While strong boards can be made of excelsior fibres when they arecompacted under pressure with a suitable binder, it is, for allpractical purposes, impossible to disentangle the long, curly excelsiorfibres and then to distribute them evenly in a form so that theresultant board will be of uniform density. Moreover, the cost ofcutting excclsior fibres is competitively prohibitive.

On the other hand, while boards of uniform density and relativelyuniform surface texture can be made when certain wood granules, such asfine sawdust and shavings, are used, the mechanical properties of theresultant bglards are so deficient that they have no commercial v ue.

Certain s e i l ufibres such as those obtained by the A s lundrocessoil'iibration,- and fibre u on a Mac- Millan 'm'iah'i'na as well asm'echanical and chemical aer' ul Have been sugg'sT-fi"'oiqqrTfTt'i-iii'eTgi'it"A Ell goars lmade with these lack the necessary strengthin competition with established products.

The following table gives the results of strength tests made on 3/i-inchboards in which three parts of sum by weight, were combined with onepart of Wild the same quantities were used for all boards. surfaces ofal1 the boards were faced with a thin layer of gypsum to obtain perfectsmoothness. The tests were made on specimens S inches wide and 12incheslong, supported on a span of inches and loaded progressively witha center load. Load-deflection curves were plotted, and the area underthese curves was measured to obtain the work done to produce completefailure. The latter measures the toughness of the board and its abilityto absorb a blow.

It will be seen from this table that the boards made with the shavingstrands are several times as strong as those made with any of the otherfibre types, and that they are about ten times as tough as the averagetoughness of the other boards.

Careful analysis of the results showed that thoroug mixing of theAsplund fibres to obtain complete separation and coating of'all thefibres is difficult to obtain. Such fibres tend to clump in tufts.Sawdust particles are short and broken granules lacking in fibrestrength but readily lending themselves to even spreading and coating.Shavings and MacMillan fibres have a common characteristic whichapparently reduces their strength in comparison with the shavingstrands, a characteristic of all Shavings produced by a rotating'cuttingedge, namely, weakness due to the fact that the direction of the knifeparallel to the direction of the botanical wood fibres of which theshavings are composed. Most of the cut is diagonally across the grain ofthe wood fibres, with the result that the full strength of the wood islost. This is less true of the MacMillan bre, on account of the largerradius of the swing of the cutting edge, and, as will be seen from thedata, the resultant MacMillan breboards are also stronger than thosemade of ordinary ne planer Shavings. I have found that, for maximumstrength, the cut must be substantially parallel to the botanic woodfibres throughout the strand length, and that the average length of theresultant strand-like shavings must be at least 1/2 inch. The shavingstrands should preferably be straight in order to obtain uniformreinforcement and distribution, and they should preferably be very thinto obtain a good bonding area for a given weight of fibres. Such strandshave practically the full tensile strength of the wood, which ordinaryShavings do not.

Excessively long strands also result in non-uniformity. An averagelength greater than 6 inches sngplgl be avoided. Strands Oo-mc t ic wipara el sur aces, give good results. The edges of the strands need notbe parallel.

Various ratios of binder or ma rix ei t t str d wei ht may e e ngingroma ou o u' out l'l'l'mlft On account of greater facility of cuttingthe resultant board, and its lightness, the lower ratios are preferredfor boards intended for interior use. Boards having Pgtlagg gement asthe matrix, and intended for exterio use, w ere t eyare exposed to theweather, are preferably made with the higher ratios.

The following table shows the results of tests made to compare thestrength and stiffness of the gypsum shaving strand board with ordinarygypsum paper-faced board of about the same thickness:

Transverse test [Zest's ecimen 3" wide tested on 4" s an. Ordinarygypsum Tests were made to compare the lire resistance of the gypsumstrand board with conventional paper-faced gypsum board. Specimens 3inches wide were supported on a S-inch span with a small center load ofless than 1 pound, and a broad Bunsen burner flame was allowed to playon the bottom of the specimen directly under the load. The time requiredfor collapse to take place was noted. Ordinary paper-faced boardscollapse in this test in less than 4 minutes, whereas the gypsum strandboards hold up for 13 minutes.

Tests were made to determine the resistance of the boards to the pull ofnails, by measuring the force required to pull a nail down into theboard to submerge the nail head. The pull in pounds is given in thefollowing table.

Cadmium o Coated Nail Product Head Diameter0.21

meh eter-.095

inch

Gypsum strand board 302 B6 Ordinary gypsum board w 35 Thus the gypsumstrand board of the present invention can be applied with a much smallerheaded nail, eliminating disgurement, and obtaining, meanwhile, the sameholding strength as is obtained with the large headed nail used withcommercial paper-faced gypsum board.

I also obtain a cost saving. The shaving strands produced in a machinebuilt for the purpose cost only about one-sixth as much per ton as thethick paper faces used for ordinary gypsum boards. The cost of allmaterials per square foot of board is substantially less than thetaldcost of the materials that go into ordinary gypsum ar s.

-It will be realized that whereas I have described a practical andoperative embodiment of my invention, nevertheless many changes may bemade without departing from the spirit of my invention. The species ofthe strands and their length and width may be widely varied. They may bemade of various woods. The inorganic binder or matrix in which thefibres are embedded may be of a wide variety of materials. The thicknessof the board and also the thickness of the smooth plaster coating may bevaried. Some variation in density may be tolerated without deviatingfrom the spirit of the invention. Whereas an advantage of my inventionis that a paper covering or outer layer is unnecessary, I may still findit advantageous for manufacturing to apply a paper coating to one orboth exterior surfaces. It will be understood, also, that I may make myboard by a variety of methods, as by continuous pressing between movingbelts, or by means of stationary plate pressure. Nor do I limit myselfto any particular method or mechanism for producing the strandsthemselves. However, it is essential that the strands be cut with thebotanic bres substantially parallel to tl:1 surface of the strandsthemselves throughout their leng It will be understood that when Iemploy the term ent I wish it to be interpreted with sufficient breadthto include any inorganic binder, including those which set due to theformation of crystals from a supersaturated aqueous solution, forexample, Portland cement, gypsum and ma nesite cement.

I'hls appllcat-ion i"s a continuation-in-part of my application SerialNo. 218,862, led April 2, 1951, for Embedded Fibre Wallboard, nowabandoned.

I claim:

1. A nonporous wallboard structure having a body formed of a relativelysolid, nonporous matrix of a material selected from the class ofinorganic cements including gypsum, Portland cement and magnesitecement, said matrix having a plurality of wood strands embedded therein,each strand having the botanic fibres thereof substantially parallel tothe surfaces of the strand and generally parallel to the strand length,the weight of said matrix exceeding the weight of said strands, thelength of the strands, on an average, exceeding one-half inch whilebeing less than six inches.

2. A nonporous wallboard structure having Ia body formed of a relativelysolid, nonporous matrix of a material selected from the class ofinorganic cements including gypsum, Portland cement and magnesitecement, said matrix having a plurality of wood strands embedded therein,each strand having the botanic bres thereof substantially parallel tothe surfaces of the strand and generally parallel to the strand length,the weight of said matrix exceeding the weight of said strand, thelength of the strands,

on an average, exceeding one-half inch While being less than six inches,and the width of the strands, on an average, being substantially lessthan their length.

3. A nonporous wallboard structure having a body formed of a relativelysolid, nonporous matrix of material selected from the class of inorganiccements including gypsum, Portland cement and magnesite cement, saidmatrix having a plurality of wood strands embedded therein, each strandhaving the botanic libres thereof substantially parallel to the surfacesof the strands and generally parallel to the strand length, the weightof said matrix exceeding the weight of said strands, said body portionhaving opposed generally parallel surfaces, said body portion having acentral zone and surface zones adjacent said surfaces, said strands insaid surface zones being inclined to the planes of said body portionsurfaces at an average included angle less than 45 degrees, the lengthof the strands, on an average, exceeding one-half inch while being lessthan six inches.

4. A nonporous wallboard structure having a body formed of a relativelysolid, nonporous matrix of a material selected from the class ofinorganic cements, including gypsum, Portland cement and magnesitecement, said matrix having a plurality of wood strands embedded therein,each strand being substantially straight and having the botanic fibresthereof substantially parallel to at least one surface of the strand andgenerally parallel to the strand length, the weight of said matrixexceeding the weight of said strands, said body portion having opposedgenerally parallel surfaces, said body having a central portion in whichthe volume of the strands exceeds the volume of the cement, and outerportions near the surfaces in which the volume of said cement exceedsthe volume of said strands, the length of the strands, on an averageexceeding one-half inch While being less than six inches.

5. A nonporous wallboard as set forth in claim 4 wherein at least oneface of the wallboard is surfaced with a thin layer of cement completelyfree from libres.

6. A nonporous wallboard as set forth in claim 4 characterized by andincluding one surface of the wallboard having a thin layer of cementcompletely free from strands, some of said strands extending withsufficient proximity to said surface that they are visible through saidsurface.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 1,303,313 Herbert May 13, 1919 1,423,569 Lockhart July 25,1922 1,500,207 Shaw July 8, 1924 2,066,734 Loetscher Jan. 5, 19372,332,703 Elmendorf Oct. 26, 1943 2,392,844 Fairchild Jan. 15, 19462,446,304 Roman Aug. 3, 1948 2,539,904 Hansen Jan. 30, 1951 FOREIGNPATENTS Number Country Date 608,252 Great Britain Sept. 13, 1948 OTHERREFERENCES Wood Fibers From Veneer Waste, article by Armin Elmendorf,published in Paper Trade Journal for February 9, 1950.

1. A NONPOROUS WALBOARD STRUCTURE HAVING A BODY FORMED OF A RELATIVELYSOLID, NONPOROUS MATRIX OF A MATERIAL SELECTED FROM THE CLASS OFINORGANIC CEMENTS INCLUDING GYPSUM, PORTLAND CEMENT AND MAGNESITECEMENT, SAID MATRIX HAVING A PLURALITY OF WOOD STRANDS EMBEDDED THEREIN,EACH STRAND HAVING THE BOTANIC FIBERS THEREOF SUBSTANTTIALLY PARALLEL TOTHE SURFACES OF THE STRAND AND GENERALLY PARALLEL TO THE STRAND LENGTH,THE WEIGHT OF SAID MATRIX EXCEEDING THE WEIGHT OF SAID STRANDS, THELENGTH OF THE STRANDS, ON AN AVERAGE, EXCEEDING ONE-HALF IN WHILE BEINGLESS THAN SIX INCHES.